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Milwaukee County

New wastewater discharge permit requires 'green infrastructure'

Chris Wilson

Anthony Mayer, CEO of Hanging Gardens LLC, checks the irrigation system at the recently planted green roof on the Mitchell Street Market Lofts on Wednesday in Milwaukee. The green roof, which covers 16,334 square feet on two levels, is capable of storing thousands of gallons of storm water.

You would expect state permits for municipal sewage plants to limit the amount of pollutants discharged to rivers and lakes and to impose deadlines on upgrading sewers and treatment facilities.

But a draft state wastewater discharge permit for the Milwaukee Metropolitan Sewerage District is the first in the U.S. to add this regulatory wrinkle: requiring rooftop plantings and installation of other "green infrastructure" - not sewer pipes or storage tunnels - to collect and absorb storm water.

Compliance with the requirement will result in more rain barrels and rain gardens at homes, porous pavement in parking lots, thick coverings of plants on flat rooftops, landscaped swales on the sides of streets and additional district purchases of wetlands and floodplains.

MMSD must work with municipalities and private property owners to add the equivalent of 1 million gallons worth of storage capacity in such projects each year, under terms of the draft permit. Taxpayers will be paying a portion of each project's cost in the district's annual construction budgets.

Primary reasons for the mandate include cutting the number and volume of sewer overflows to waterways and reducing risk of sewage backups into basements, said Ted Bosch, wastewater engineer with the state Department of Natural Resources in Milwaukee.

The cost of green storage compares favorably to digging more tunnels, Sands said. But the dual benefit to taxpayers is that each project reduces flows to sewers while building storage capacity, she said.

In 2012 and 2013, the district has budgeted slightly more than $2.95 million each year for all green infrastructure spending.

Digging more tunnels to store wastewater would cost nearly $2.50 for a gallon of capacity. Porous pavement costs around 35 cents a gallon of capacity. The district's share of a green roof - now $5 a square foot - is around $1.10 a gallon of capacity, though total cost for the property owner is higher.

This permit requirement ties in to the district's goal of no sewer overflows by 2035, Sands said. From the first year of deep tunnel operation in 1994 through 2011, there has been an average of 2.5 overflows a year in the combined sanitary and storm sewers of central Milwaukee and eastern Shorewood.

More than rain barrels

Directing a home's downspout into a 200-square-foot rain garden planted with deep-rooted flowers and grasses will provide up to 600 gallons of storage.

Even larger volumes are being captured on Milwaukee rooftops where the district has helped pay for plantings.

At Rockwell Automation's global headquarters on S. 2nd. St., two dozen varieties of sedum, native wildflowers and perennials growing in soil and peat moss collect 40,000 gallons or more of water in each storm.

The 48,500-square-foot green roof in the shadow of the Allen-Bradley clock tower was completed in October 2010 and is the largest in Wisconsin on a single level.

Monitors show the project collects more than 70% of all rain that falls, said Majo Thurman, the company's safety and environmental director. This roof captures the first inch and a quarter of a rainfall.

Between June 2010 and June 2012, Rockwell's plantings absorbed 500,000 gallons of water, Thurman said.

Other green roof designs are capable of capturing even more water - up to 3 gallons per square foot.

At the Mitchell Street Market Lofts affordable housing project in the 1900 block of W. Mitchell St., a dozen varieties of sedum were planted at the end of June, covering 16,334 square feet on two levels. "This green roof will collect 90% of rainfall in an average year." said Anthony Mayer, chief executive officer of Hanging Gardens LLC. The company installed the rooftop plantings for developer Impact Seven Inc.

Since 2003, MMSD has been awarding grants to building owners to encourage plantings of green roofs. They can be found on Milwaukee's Central Public Library and the Golda Meir Library on the University of Wisconsin-Milwaukee campus.

The district contributed $808,584 to Rockwell and will spend an estimated $161,000 at the Mitchell St. lofts to help pay for those projects.

Under terms of the new state permit, MMSD would get credit for 3 gallons a square foot, or 49,002 gallons of storm water capacity for the Mitchell project.

Next month, a green roof will be planted on 9,627 square feet of Badger Meter's corporate headquarters in the 4500 block of W. Brown Deer Road. The district is paying a straight $5 a square foot for the project, giving it credit for 28,881 gallons of green capacity under the permit.

There are bigger guns available for MMSD to help meet the new mandate.

One is porous, or permeable, pavement. Converting one acre of old-style concrete or asphalt parking lot to a porous design captures up to 435,600 gallons of storm water.

Buying an acre of open space at a wetland or in a river's floodplain as part of the district's Greenseams conservation program will add between 65,000 and 651,000 gallons of storage to the green infrastructure total.

From 2002 through 2011, there has been an average of 118 million gallons worth of green infrastructure storage built in the Milwaukee area, according to Sands.

"We've been implementing green infrastructure for several years to help reduce sewer overflows and improve water quality," MMSD Executive Director Kevin Shafer said.

MMSD's permit requirement is "the first of its kind in the United States," said Ben Grumbles, president of the Clean Water America Alliance and a former assistant administrator for water at the U.S. Environmental Protection Agency.

While the EPA has imposed limited green infrastructure investments on municipal sewerage districts as part of consent orders in the wake of permit violations, no other district faces such a mandate in its operating permit, he said.

The DNR has scheduled a public hearing on the proposed MMSD discharge permit beginning at 1 p.m. Thursday in the department's southeast region headquarters, 2300 N. King Drive, Milwaukee.

About Don Behm

Don Behm reports on the environment, Milwaukee Metropolitan Sewerage District and communities in southeastern Wisconsin. Behm has won reporting awards for investigations of Great Lakes water pollution, improper disposal of radioactive waste from nuclear weapons production, Milwaukee's cryptosporidiosis outbreak and the deaths of three sewer construction workers in a Menomonee Valley methane explosion.